Wakeup radio (wur) preamble design

ABSTRACT

A communication device generates a first portion of a wakeup packet that corresponds to a legacy physical layer protocol (PHY) preamble, and includes a first orthogonal frequency division multiplexing (OFDM) symbol that spans a first bandwidth and is modulated according to a modulation scheme. The communication device scrambles a plurality of information bits to generate scrambled information bits, and generates a second OFDM symbol to include the scrambled information bits. The second OFDM symbol spans the first bandwidth and is modulated according to the modulation scheme to signal to other communication devices that the wakeup packet does not conform to a communication protocol. The first communication device generates a second portion of the wakeup packet, which corresponds to a second bandwidth that is less than the first bandwidth. The communication device transmits the second OFDM symbol between the first portion of the wakeup packet and the second portion of the wakeup packet.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/985,480, entitled “Wakeup Radio (WUR) Preamble Design,” filed on May21, 2018, which claims the benefit of U.S. Provisional PatentApplication No. 62/511,516, entitled “Wakeup Radio (WUR) PreambleDesign,” filed on May 26, 2017. Both of the applications referencedabove are incorporated herein by reference in their entireties.

FIELD OF TECHNOLOGY

The present disclosure relates generally to wireless communicationsystems, and more particularly to wireless communication systemsutilizing low power wakeup radios to implement power saving features.

BACKGROUND

Wireless local area networks (WLANs) have evolved rapidly over the pastdecade, and development of WLAN standards such as the Institute forElectrical and Electronics Engineers (IEEE) 802.11 Standard family hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughput, such as throughputs in the tens of Gbps range.

Some WLANs include low cost wireless devices, such as wireless sensors,that do not require high data rates. To reduce operating costs, it maybe useful for such wireless devices to be battery operated or otherwisepower constrained. Power saving techniques for reducing powerconsumption are used with such power-constrained wireless devices. Forexample, a WLAN network interface of a power-constrained wireless deviceis put into to a low power state (e.g., a sleep state) for periods oftime in order to decrease power consumption of the wireless device. Whenthe wireless device is ready to transmit data to an access point, theWLAN network interface is transitioned to an active state so that thedata can be transmitted. After the WLAN network interface transmits thedata, the WLAN network interface transitions back to the low powerstate.

A WLAN network interface of a power-constrained wireless device may“wake up” periodically to listen for transmissions from the access pointto determine whether the access point has data to transmit to thewireless device. However, such periodic “wake ups” by the WLAN networkinterface consume power even when the access point has no data totransmit to the wireless device. Therefore, to further reduce powerconsumption, some wireless devices employ a low power wake up radio(LP-WUR) that consumes much less power as compared to the WLAN networkinterface. For example, the LP-WUR does not include any transmittercircuitry and may be capable of only receiving very low data ratetransmissions. When the access point is ready to transmit data to thewireless device, the access point transmits a wakeup packet addressed tothe wireless device. In response to receiving the wakeup packet anddetermining that the wakeup packet is addressed to the wireless device,the LP-WUR wakes up the WLAN network interface so that the WLAN networkinterface is ready to receive data from the access point.

SUMMARY

In an embodiment, a method includes: generating, at the firstcommunication device, a first portion of a wakeup packet, wherein thefirst portion of the wakeup packet corresponds to a legacy physicallayer protocol (PHY) preamble corresponding to a communication protocol,wherein the first portion of the wakeup packet includes a firstorthogonal frequency division multiplexing (OFDM) symbol that spans afirst bandwidth and is modulated according to a modulation scheme;generating, at the first communication device, a second OFDM symbol,wherein the second OFDM symbol spans the first bandwidth and ismodulated according to the modulation scheme; generating, at the firstcommunication device, a second portion of the wakeup packet, wherein thesecond portion of the wakeup packet corresponds to a second bandwidththat is less than the first bandwidth, and wherein the second portion ofthe wakeup packet does not conform to the communication protocol; andtransmitting, by the first communication device, the wakeup packet,including transmitting, in time, the second OFDM symbol between thefirst portion of the wakeup packet and the second portion of the wakeuppacket, and wherein the modulation of the second OFDM symbol accordingto the modulation scheme signals to third communication devicesoperating according to the communication protocol that the wakeup packetdoes not conform to the communication protocol.

In another embodiment, an apparatus comprises a network interface deviceassociated with a first communication device. The network interfacedevice includes one or more integrated circuits (ICs) configured to:generate a first portion of a wakeup packet, wherein the first portionof the wakeup packet corresponds to a legacy PHY preamble correspondingto a communication protocol, wherein the first portion of the wakeuppacket includes a first OFDM symbol that spans a first bandwidth and ismodulated according to a modulation scheme, generate a second OFDMsymbol, wherein the second OFDM symbol spans the first bandwidth and ismodulated according to the modulation scheme, generate a second portionof the wakeup packet, wherein the second portion of the wakeup packetcorresponds to a second bandwidth that is less than the first bandwidth,and wherein the second portion of the wakeup packet does not conform tothe communication protocol. The one or more ICs are also configured totransmit the wakeup packet, including transmitting, in time, the secondOFDM symbol between the first portion of the wakeup packet and thesecond portion of the wakeup packet. The modulation of the second OFDMsymbol according to the modulation scheme signals to third communicationdevices operating according to the communication protocol that thewakeup packet does not conform to the communication protocol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an example wireless local area network(WLAN) having a client station with a low power wake up radio (LP-WUR),according to an embodiment.

FIG. 1B is a block diagram of an example wireless network interfacedevice of an access point included in the WLAN of FIG. 1A, according toan embodiment.

FIG. 1C is a block diagram of an example wireless network interfacedevice of the client station included in the WLAN of FIG. 1A, accordingto an embodiment.

FIG. 1D is a block diagram of an example LP-WUR in the WLAN of FIG. 1A,according to an embodiment.

FIG. 2 is a block diagram of a prior physical layer protocol (PHY) dataunit.

FIG. 3 is a diagram of a modulation scheme used to modulate fields inthe prior art PHY data unit of FIG. 2.

FIG. 4 is a block diagram of another prior art PHY data unit.

FIG. 5 is a diagram of a modulation scheme used to modulate fields inthe prior art PHY data unit of FIG. 4.

FIG. 6 is a block diagram of an example wakeup packet, according to anembodiment.

FIG. 7 is a block diagram of another example wakeup packet, according toanother embodiment.

FIG. 8 is a diagram of a modulation scheme used to modulate fields inthe example wakeup packet of FIG. 7, according to an embodiment.

FIG. 9 is a flow diagram of an example method for generating wakeuppackets, according to an embodiment.

DETAILED DESCRIPTION

Low power wakeup techniques described below are discussed in the contextof wireless local area networks (WLANs) that utilize protocols the sameas or similar to protocols defined by the 802.11 Standard from theInstitute of Electrical and Electronics Engineers (IEEE) merely forexplanatory purposes. In other embodiments, however, the same or similarpower saving techniques are utilized in other types of wirelesscommunication systems such as personal area networks (PANs), mobilecommunication networks such as cellular networks, metropolitan areanetworks (MANs), satellite communication networks, etc.

In embodiments described below, an access point (AP) is configured totransmit a wakeup request packet to one or more client stations, causingthe one or more client stations to transition from a low power state toan active state. In various embodiments, frame formats for wakeuppackets are configured to avoid compatibility issues in communicationnetworks that include multiple devices operating according to differentcommunication protocols.

FIG. 1A is a block diagram of an example WLAN 110, according to anembodiment. The WLAN 110 includes an access point (AP) 114 thatcomprises a host processor 118 coupled to a wireless network interfacedevice 122. The wireless network interface device 122 is coupled to aplurality of antennas 126. Although three antennas 126 are illustratedin FIG. 1A, the AP 114 includes other suitable numbers (e.g., 1, 2, 4,5, etc.) of antennas 126 in other embodiments. As will be described inmore detail below, the wireless network interface device 122 isconfigured to generate and transmit a wakeup packet that can be decodedby low power wake up radios (LP-WURs) in the WLAN 110.

The host processor 118 is configured to executed machine readableinstructions stored in a memory device (not shown), according to anembodiment. The host processor 118 is implemented on an integratedcircuit (IC), according to an embodiment. The wireless network interfacedevice 122 is implemented on one or more ICs. The host processor 118 isimplemented on one IC and the wireless network interface device 122 isimplemented on one or more other, different ICs, according to anembodiment. The host processor 118 is implemented on a first IC and thewireless network interface device 122 is implemented on at least thesame first IC and optionally on one or more second ICs, according to anembodiment.

The WLAN 110 also includes one or more client stations 134. Althoughthree client stations 134 are illustrated in FIG. 1A, the WLAN 110includes other suitable numbers (e.g., 1, 2, 4, 5, 6, etc.) of clientstations 134 in various embodiments. The client station 134-1 includes ahost processor 138 coupled to a wireless network interface device 142.The wireless network interface device 142 is coupled to one or moreantennas 146. Although three antennas 146 are illustrated in FIG. 1A,the client station 134-1 includes other suitable numbers (e.g., 1, 2, 4,5, etc.) of antennas 146 in other embodiments.

The wireless network interface device 142 is configured to go into a lowpower state in which the wireless network interface device 142 consumessignificantly less power as compared to an active state of the wirelessnetwork interface device 142. The wireless network interface device 142is capable of wirelessly receiving and transmitting via the one or moreantennas 146 while in the active state. In an embodiment, the wirelessnetwork interface device 142 is incapable of wirelessly receiving andtransmitting via the one or more antennas 146 while in the low powerstate.

The client station 134-1 also includes a LP-WUR 150 coupled to thewireless network interface device 142 and to at least one of theantennas 146. The LP-WUR 150 is configured to use very low power (e.g.,less than 100 microwatts or another suitable amount of power). TheLP-WUR 150 is configured to use significantly less power (e.g., lessthan 20%, less than 10%, less than 5%, less than 2%, less than 1%, etc.)than the wireless network interface device 142 while the wirelessnetwork interface device 142 is in the active state, according to anembodiment.

The LP-WUR 150 is configured to operate over a smaller bandwidth (e.g.,less than 50%, less than 25%, less than 20%, less than 10%) than theoperating bandwidth of the wireless network interface device 142 whilethe wireless network interface device 142 is in the active state, in anembodiment. For instance, in an embodiment, the LP-WUR 150 operates overa communication channel that is approximately 4 MHz wide (e.g. 4.06 MHzwide) while the wireless network interface device 142, in an activestate, operates over a wider communication channel that is 20 MHz wide.In an embodiment, the LP-WUR 150 operates over a communication channelthat is centered within the communication channel corresponding to theoperating bandwidth of the wireless network interface device 142. Inanother embodiment however, the LP-WUR 150 is configured to operate overa bandwidth that is equal or substantially equal to an operatingbandwidth of the wireless network interface device 142 while thewireless network interface device 142 is in the active state. In anembodiment, the wireless network interface device 142, in an activestate, is further configured to operate over a communication channelthat is wider than 20 MHz (e.g., 40 MHz, 80 MHz, 160 MHz, etc.).

The LP-WUR 150 is configured to receive and decode wakeup packetstransmitted by the AP 114 and received via one or more of the antennas146. The LP-WUR 150 is configured to determine whether a received wakeuppacket includes an address (e.g., a media access control (MAC) address,an association identifier (AID), or another suitable network address)corresponding to the client station 134-1, according to an embodiment.The LP-WUR 150 is configured to generate a wakeup signal in response todetermining that a received wakeup packet includes the addresscorresponding to the client station 134-1.

When the wireless network interface device 142 is in the low power stateand receives the wakeup signal from the LP-WUR 150, the wireless networkinterface device 142 is configured to transition to the active powerstate in response to the wakeup signal, according to an embodiment. Forexample, when the wireless network interface device 142 is in the lowpower state and receives the wakeup signal from the LP-WUR 150, thewireless network interface device 142 responsively transitions to theactive power state to become ready to transmit and/or receive, accordingto an embodiment.

The host processor 138 is configured to executed machine readableinstructions stored in a memory device (not shown), according to anembodiment. The host processor 138 is implemented on an IC, according toan embodiment. The wireless network interface device 142 is implementedon one or more ICs. The host processor 138 is implemented on one IC andthe wireless network interface device 142 is implemented on one or moreother, different ICs, according to an embodiment. The host processor 138is implemented on a first IC and the wireless network interface device142 is implemented on at least the same first IC and optionally on oneor more second ICs, according to an embodiment.

The LP-WUR 150 is implemented on one IC and the wireless networkinterface device 142 is implemented on one or more other, different ICs,according to an embodiment. The LP-WUR 150 is implemented on a first ICand the wireless network interface device 142 is implemented on at leastthe same first IC and optionally on one or more second ICs, according toan embodiment.

In an embodiment, each of the client stations 134-2 and 134-3 has astructure that is the same as or similar to the client station 134-1.For example, one or both of the client stations 134-2 and 134-3 includesa respective LP-WUR, according to an embodiment. As another example, oneor both of the client stations 134-2 and 134-3 does not include aLP-WUR, according to another embodiment. Each of the client stations134-2 and 134-3 has the same or a different number of antennas (e.g., 1,2, 3, 4, 5, etc.). For example, the client station 134-2 and/or theclient station 134-3 each have only two antennas (not shown), accordingto an embodiment.

FIG. 1B is a block diagram of the network interface device 122 of the AP114 of FIG. 1A, according to an embodiment. The network interface device122 includes a MAC layer processor 160 coupled to a physical layer (PHY)processor 164. The PHY processor 164 includes a plurality oftransceivers 168 coupled to the plurality of antennas 126. Althoughthree transceivers 168 and three antennas 126 are illustrated in FIG.1B, the PHY processor 164 includes other suitable numbers (e.g., 1, 2,4, 5, etc.) of transceivers 168 coupled to other suitable numbers ofantennas 126 in other embodiments. In some embodiments, the AP 114includes a higher number of antennas 126 than transceivers 168, and thePHY processor 164 is configured to use antenna switching techniques.

The network interface device 122 is implemented using one or more ICsconfigured to operate as discussed below. For example, the MAC layerprocessor 160 may be implemented, at least partially, on a first IC, andthe PHY processor 164 may be implemented, at least partially, on asecond IC. As another example, at least a portion of the MAC layerprocessor 160 and at least a portion of the PHY processor 164 may beimplemented on a single IC. For instance, the network interface device122 may be implemented using a system on a chip (SoC), where the SoCincludes at least a portion of the MAC layer processor 160 and at leasta portion of the PHY processor 164.

In various embodiments, the MAC layer processor 160 and/or the PHYprocessor 164 of the AP 114 are configured to generate data units, andprocess received data units, that conform to a WLAN communicationprotocol such as a communication protocol conforming to the IEEE 802.11Standard or another suitable wireless communication protocol. Forexample, the MAC layer processor 160 may be configured to implement MAClayer functions, including MAC layer functions of the WLAN communicationprotocol, and the PHY processor 164 may be configured to implement PHYfunctions, including PHY functions of the WLAN communication protocol.For instance, the MAC layer processor 160 may be configured to generateMAC layer data units such as MAC service data units (MSDUs), MACprotocol data units (MPDUs), etc., and provide the MAC layer data unitsto the PHY processor 164. The PHY processor 164 may be configured toreceive MAC layer data units from the MAC layer processor 160 andencapsulate the MAC layer data units to generate PHY data units such asPHY protocol data units (PPDUs) for transmission via the antennas 126.Similarly, the PHY processor 164 may be configured to receive PHY dataunits that were received via the antennas 126, and extract MAC layerdata units encapsulated within the PHY data units. The PHY processor 164may provide the extracted MAC layer data units to the MAC layerprocessor 160, which then processes the MAC layer data units.

In connection with generating one or more radio frequency (RF) signalsfor transmission, the PHY processor 130 is configured to process (whichmay include modulating, filtering, etc.) data corresponding to a PPDU togenerate one or more digital baseband signals, and convert the digitalbaseband signal(s) to one or more analog baseband signals, according toan embodiment. Additionally, the PHY processor 130 is configured toupconvert the one or more analog baseband signals to one or more RFsignals for transmission via the one or more antennas 138.

In connection with receiving one or more signals RF signals, the PHYprocessor 130 is configured to downconvert the one or more RF signals toone or more analog baseband signals, and to convert the one or moreanalog baseband signals to one or more digital baseband signals. The PHYprocessor 130 is further configured to process (which may includedemodulating, filtering, etc.) the one or more digital baseband signalsto generate a PPDU.

The PHY processor 130 includes amplifiers (e.g., a low noise amplifier(LNA), a power amplifier, etc.), a radio frequency (RF) downconverter,an RF upconverter, a plurality of filters, one or more analog-to-digitalconverters (ADCs), one or more digital-to-analog converters (DACs), oneor more discrete Fourier transform (DFT) calculators (e.g., a fastFourier transform (FFT) calculator), one or more inverse discreteFourier transform (IDFT) calculators (e.g., an inverse fast Fouriertransform (IFFT) calculator), one or more modulators, one or moredemodulators, etc.

The PHY processor 164 is configured to generate one or more RF signalsthat are provided to the one or more antennas 126. The PHY processor 164is also configured to receive one or more RF signals from the one ormore antennas 126.

The MAC processor 160 is configured to control the PHY processor 164 togenerate one or more RF signals by, for example, providing one or moreMAC layer data units (e.g., MPDUs) to the PHY processor 164, andoptionally providing one or more control signals to the PHY processor164, according to some embodiments. In an embodiment, the MAC processor160 includes a processor configured to execute machine readableinstructions stored in a memory device (not shown) such as a RAM, a readROM, a flash memory, etc. In an embodiment, the MAC processor 160includes a hardware state machine.

FIG. 1C is a block diagram of the network interface device 142 of theclient station 134-1 of FIG. 1A, according to an embodiment. The networkinterface device 142 includes a MAC layer processor 172 coupled to a PHYprocessor 174. The PHY processor 174 includes a plurality oftransceivers 178 coupled to the one or more antennas 146. Although threetransceivers 178 and three antennas 126 are illustrated in FIG. 1C, thePHY processor 174 includes other suitable numbers (e.g., 1, 2, 4, 5,etc.) of transceivers 178 coupled to other suitable numbers of antennas146 in other embodiments. In some embodiments, the client station 134-1includes a higher number of antennas 146 than transceivers 178, and thePHY processor 174 is configured to use antenna switching techniques.

The network interface device 142 is implemented using one or more ICsconfigured to operate as discussed below. For example, the MAC layerprocessor 172 may be implemented, at least partially, on a first IC, andthe PHY processor 174 may be implemented, at least partially, on asecond IC. As another example, at least a portion of the MAC layerprocessor 172 and at least a portion of the PHY processor 174 may beimplemented on a single IC. For instance, the network interface device142 may be implemented using a system on a chip (SoC), where the SoCincludes at least a portion of the MAC layer processor 172 and at leasta portion of the PHY processor 174.

In various embodiments, the MAC layer processor 172 and the PHYprocessor 174 of the client station 134-1 are configured to generatedata units, and process received data units, that conform to the WLANcommunication protocol such as a communication protocol conforming tothe IEEE 802.11 Standard or another suitable wireless communicationprotocol. For example, the MAC layer processor 172 may be configured toimplement MAC layer functions, including MAC layer functions of the WLANcommunication protocol, and the PHY processor 174 may be configured toimplement PHY functions, including PHY functions of the WLANcommunication protocol. The MAC layer processor 172 may be configured togenerate MAC layer data units such as MSDUs, MPDUs, etc., and providethe MAC layer data units to the PHY processor 174. The PHY processor 174may be configured to receive MAC layer data units from the MAC layerprocessor 172 and encapsulate the MAC layer data units to generate PHYdata units such as PPDUs for transmission via the one or more antennas146. Similarly, the PHY processor 174 may be configured to receive PHYdata units that were received via the one or more antennas 146, andextract MAC layer data units encapsulated within the PHY data units. ThePHY processor 174 may provide the extracted MAC layer data units to theMAC layer processor 172, which then processes the MAC layer data units.

As discussed above, the network interface device 142 is configured totransition between an active state and a low power state. When thewireless network interface device 142 is in the low power state andreceives the wakeup signal from the LP-WUR 150, the wireless networkinterface device 142 is configured to transition to the active powerstate in response to the wakeup signal, according to an embodiment.

The PHY processor 174 is configured to downconvert one or more RFsignals received via the one or more antennas 146 to one or morebaseband analog signals, and convert the analog baseband signal(s) toone or more digital baseband signals, according to an embodiment. ThePHY processor 174 is further configured to process the one or moredigital baseband signals to demodulate the one or more digital basebandsignals and to generate a PPDU. The PHY processor 174 includesamplifiers (e.g., an LNA, a power amplifier, etc.), an RF downconverter,an RF upconverter, a plurality of filters, one or ADCs, one or moreDACs, one or more DFT calculators (e.g., a fast Fourier transform (FFT)calculator), one or more IDFT calculators (e.g., an inverse fast Fouriertransform (IFFT) calculator), one or more modulators, one or moredemodulators, etc.

The PHY processor 174 is configured to generate one or more RF signalsthat are provided to the one or more antennas 146. The PHY processor 174is also configured to receive one or more RF signals from the one ormore antennas 146.

The MAC processor 172 is configured to control the PHY processor 174 togenerate one or more RF signals by, for example, providing one or moreMAC layer data units (e.g., MPDUs) to the PHY processor 174, andoptionally providing one or more control signals to the PHY processor174, according to some embodiments. In an embodiment, the MAC processor172 includes a processor configured to execute machine readableinstructions stored in a memory device (not shown) such as a RAM, a readROM, a flash memory, etc. In an embodiment, the MAC processor 172includes a hardware state machine.

FIG. 1D is a block diagram of the LP-WUR 150 of the client station 134-1of FIG. 1A, according to an embodiment. The LP-WUR 150 includes radiofrequency (RF)/analog front-end circuitry 184 coupled to at least one ofthe antennas 146. The RF/analog front-end circuitry 184 includes one ormore amplifiers (e.g., a low noise amplifier (LNA)), an RFdownconverter, one or more filters, and one or more analog-to-digitalconverters (ADCs). In an embodiment, the RF/analog front-end circuitry184 is configured to downconvert an RF signal to a baseband analogsignal, and convert the analog baseband signal to a digital basebandsignal.

The RF/analog front-end circuitry 184 is coupled to digital basebandcircuitry 188. The digital baseband circuitry 188 is configured toprocess the digital baseband signal to determine whether the digitalbaseband signal corresponds to a wakeup packet. The digital basebandcircuitry 188 includes a demodulator that demodulates data from thedigital baseband signal to generate an information signal correspondingto information included in a wakeup packet.

The digital baseband circuitry 188 is coupled to logic circuitry 192.The logic circuitry 192 is configured to process the information signalto determine whether a wakeup packet includes an address (e.g., a MACaddress, an AID, or another suitable network address) corresponding tothe client station 134-1, according to an embodiment. The logiccircuitry 192 is configured to generate the wakeup signal in response todetermining that a received wakeup packet includes the addresscorresponding to the client station 134-1. In various embodiments and/orscenarios, the network address included in the wakeup packet comprises aunicast address, a multicast address, or a broadcast address. Forexample, a broadcast network address generally corresponds to all clientstations having an LP-WUR, according to an embodiment. As anotherexample, a multicast network address corresponds to the client station134-1 if the client station 134-1 has been assigned to a group of clientstations (e.g., by the AP 114) that is associated with the multicastnetwork address, according to an embodiment. As yet another example, aunicast network address may be assigned to the client station 134-1 attime of manufacture, assigned by the AP 114 when the client station 134becomes associated with the network 110, etc., according to variousembodiments.

FIG. 2 is a diagram of a prior art PHY data unit 200 that conforms tothe IEEE 802.11n Standard.

The PHY data unit 200 includes a PHY preamble 204 preamble and a PHYdata portion 208. The PHY preamble 204 includes a legacy preambleportion 212, which includes a legacy short training field (L-STF) 216, alegacy long training field (L-LTF) 220, and a legacy signal field(L-SIG) 224. The L-STF 216 includes a defined signal (e.g., defined bythe communication protocol) generally used for packet detection, initialsynchronization, automatic gain control, etc. The L-LTF 220 includes adefined signal (e.g., defined by the communication protocol) generallyused for channel estimation, fine synchronization, etc. The L-SIG 224includes certain PHY parameters regarding the PHY data unit 200, such asa coding rate and a length, which together can be used to estimate aduration of the PHY data unit 200, according to an embodiment.

A format of the legacy portion 212 conforms to the IEEE 802.11a Standardsuch that a communication device that conforms to the IEEE 802.11aStandard and/or the IEEE 802.11g Standard (e.g., a legacy device), forexample, but does not conform to the IEEE 802.11n Standard can use thelegacy preamble 212 portion to detect the PHY data unit 200 and estimatea length of the PHY data unit 200. For example, the legacy device candetect the PHY data unit 200 by detecting the L-STF 216, for example,and can estimate a duration of the PHY data unit 200 using the L-SIG224, for example.

The PHY preamble 204 also includes a high throughput signal field(HT-SIG) 228, a high throughput short training field (HT-STF) 232, and Mhigh throughput long training fields (HT-LTFs) 236, where M is aninteger generally determined by a number of spatial streams used totransmit the data unit 200 in a multiple input multiple output (MIMO)channel configuration. In particular, according to the IEEE 802.11nStandard, the data unit 200 includes two HT-LTFs 212 if the data unit200 is transmitted using two spatial streams, and four HT-LTFs 212 ifthe data unit 200 is transmitted using three or four spatial streams. Anindication of the particular number of spatial streams being utilized isincluded in the HT-SIG field 208.

FIG. 3 is a set of diagrams illustrating a modulation 300 of the L-SIG206, the HT-SIG1 208-1, and the HT-SIG2 208-2 of the data unit 200 ofFIG. 2, as defined by the IEEE 802.11n Standard. The L-SIG 206corresponds to a first orthogonal frequency division multiplexing (OFDM)symbol, and individual tones of the first OFDM symbol are modulatedusing binary phase shift keying (BPSK). The HT-SIG1 208-1 corresponds toa second OFDM symbol, and the HT-SIG2 208-2 corresponds to a third OFDMsymbol. Individual tones of the second OFDM symbol and the third OFDMsymbol are modulated according to quaternary-BPSK (Q-BPSK). In otherwords, the modulation of tones of the HT-SIG1 208-1 and HT-SIG2 208-2 isrotated by 90 degrees as compared to the modulation of tones of theL-SIG 206.

FIG. 4 is a diagram of a prior art PHY data unit 400 that conforms tothe IEEE 802.11ac Standard.

The PHY data unit 400 includes a PHY preamble 404 preamble and a PHYdata portion 408. The PHY preamble 404 includes the legacy preambleportion 212 discussed above. A communication device that conforms to theIEEE 802.11a Standard, the IEEE 802.11g Standard, and/or the IEEE802.11n Standard (e.g., a legacy device), for example, but does notconform to the IEEE 802.11ac Standard can use the legacy preamble 212portion to detect the PHY data unit 400 and estimate a length of the PHYdata unit 400. For example, the legacy device can detect the PHY dataunit 400 by detecting the L-STF 216, for example, and can estimate aduration of the PHY data unit 200 using the L-SIG 224, for example.

The preamble 404 also includes a first very high throughput signal(VHT-SIGA) field 412 (which includes a first OFDM symbol 412-1 and asecond OFDM symbol 412-2), a very high throughput short training field(VHT-STF) 416, M very high throughput long training fields (VHT-LTFs)420, where M is an integer, and a second very high throughput signalfield (VHT-SIG-B) 424.

FIG. 5 is a set of diagrams illustrating modulation of the L-SIG 406 andthe VHT-SIGA 412, as defined by the IEEE 802.11ac Standard. Unlike theOFDM symbol 228-1 in FIG. 3, tones of the OFDM symbol 412-1 aremodulated according to BPSK, which is the same as the modulation oftones of the L-SIG 224. On the other hand, tones of the OFDM symbol412-2 are modulated using Q-BPSK, e.g., the modulation of the OFDMsymbol 412-2 is rotated by 90 degrees as compared to the modulation ofthe L-SIG 406.

FIGS. 2-4 merely illustrate some PHY data unit formats that the AP 114and the client station 134 are configured to generate and transmit in aWLAN 110. In other embodiments, the AP 114 and the client station 134are configured to generate and transmit PHY data units conforming toother standards within the IEEE 802.11 Standard family and/or PHY dataunits conforming to one or more different communication protocols.

A communication device that receives PHY data units (e.g., data unitsconforming to a communication protocol within the IEEE 802.11 Standardfamily) may need to, in certain embodiments, distinguish between PHYdata units conforming to different communication protocols (e.g., IEEE802.11a Standard, IEEE 802.11n Standard, IEEE 802.11ac Standard, etc.)in order to appropriately process the received PHY data unit. In anembodiment, detection of a digital modulation scheme (e.g., binary phaseshift keying (BPSK), quadrature binary phase shift keying (Q-BPSK),etc.), at one or more fields within a PHY preamble of the received PHYdata unit, is used for distinguishing between different communicationprotocols at a receiver. A communication device may be configured todetect the modulation (e.g., BPSK, Q-BPSK, etc.) of one or more fieldsin the PHY preamble of the received PHY data unit and classify thereceived PHY data unit as conforming to a particular communicationprotocol or not conforming to a particular communication protocol.

According to an embodiment, the network interface device 142 of theclient station 134 is capable of detecting and decoding PHY data unitsconforming to the IEEE 802.11n Standard. Thus, referring now to FIG. 2,when the network interface device 142 receives the PHY data unit 200,and the network interface device 142 detects the BPSK modulation in theL-SIG 206 and the Q-BPSK modulation in the HT-SIGs 208. Based on thedetected modulation of the L-SIG 206 and the HT-SIGs 208, the networkinterface device 142 properly classifies the received PHY data unit 200as conforming to an IEEE 802.11n Standard. When the network interfacedevice 142 receives a PHY data unit and determines that an L-SIG fieldof the PHY preamble is modulated using BPSK, and that a field followingthe L-SIG field is modulated using a digital modulation scheme that isnot Q-BPSK (e.g., BPSK), the network interface device 142 determinesthat the data unit does not conform to the IEEE 802.11n Standard.

For instance, referring now to FIG. 4, when the network interface device142 receives the PHY data unit 400 and determines that the L-SIG 406 isBPSK modulated and a field immediately following the L-SIG 406 (i.e.VHT-SIGA1 408-1) is also BPSK modulated, the network interface device142 determines that the PHY data unit 400 does not conform to the IEEE802.11n Standard. Further, if the network interface device 142 is alsocapable of detecting and decoding data units conforming to the IEEE802.11ac Standard, the network interface device 142 determines that anext field (i.e., VHT-SIGA2 field 408-2) is Q-BPSK modulated andclassifies the PHY data unit 400 as conforming to an IEEE 802.11acStandard.

The above examples refer to the network interface device 142 at a clientstation 134 utilizing detected modulation schemes at one or more fieldsin a received data unit to classify a received data unit as conformingto a particular communication protocol or not conforming to a particularcommunication protocol. While the above examples refer to PHY data unitsconforming to a standard within the IEEE 802.11 Standard family, inother embodiments, similar techniques can be utilized for classifyingdata units as conforming or not conforming to other suitablecommunication protocols.

Various mechanisms are used to prevent multiple communication devicesfrom simultaneously transmitting respective data units over a samecommunication channel. In an embodiment, communication devices in awireless network (e.g., WLAN 110) avoid simultaneously transmitting overa communication channel by using a clear channel assessment (CCA)technique to determine whether the channel is idle (i.e., available fordata transmission) or if the communication channel is busy due toanother communication device transmitting in the communication channel,in an embodiment. For instance, a communication device (e.g., the AP114, the client station 134, etc., or a network interface device 122 inthe AP 114, a network interface device 142 in the client station 134,etc.) measures a received signal energy level in the communicationchannel to determine whether the channel is idle. In an embodiment, thecommunication device, compares the received signal energy level to athreshold value and, if the received signal energy level is lower thanthe threshold value, determines that the communication channel is idleand available for data transmission.

On the other hand, if the received signal energy level is determined toexceed the threshold value, the communication device determines that thecommunication channel is busy. In an embodiment, the threshold value isset based on whether or not the received signal corresponds to a packetthat conforms to a recognized communication protocol. For instance, acommunication device compares a received signal energy level to a lowerthreshold value when it determines that the received signal correspondsto a packet that conforms to the recognized communication protocol, andcompares the received signal energy level to a higher threshold valuewhen the received signal is determined to not be a packet that conformsto the recognized communication protocol. In an embodiment, thecommunication device determines whether the received signal correspondsto a packet that conforms to the recognized communication protocol basedon whether the communication device detects the L-STF 216 in thereceived signal. In an embodiment, the communication device determineswhether the received signal corresponds to a packet that conforms to therecognized communication protocol further based on whether thecommunication device determines that received signal includes the L-SIG224 with valid data.

The IEEE 802.11 Standard provides backward compatibility features thatpermit communication devices that conform to different versions of theIEEE 802.11 Standard to interoperate. For example, the PHY data unitssuch as the PHY data unit 200 of FIG. 2 and the PHY data unit 400 ofFIG. 4 include the legacy preamble 212. The legacy preamble 212 permitslegacy devices to detect the PHY data unit 200/400 and estimate aduration of the PHY data unit 200/400 even though the legacy devices arenot able to decode other portions of the PHY data unit 200/400. When thelegacy device detects the presence and estimates the duration of the PHYdata unit 200/400, the legacy device generally refrains fromtransmitting for the estimated duration of the PHY data unit 200/400,and thus avoids interfering with the PHY data unit 200/400.

Additionally, the IEEE 802.11 Standard helps communication devices thatconform to different versions of the IEEE 802.11 Standard tointeroperate by designing PHY preambles that permit detecting to whichversion of the protocol PHY data units conform.

For instance, a legacy device that conforms to the IEEE 802.11n Standard(and does not conform to the IEEE 802.11ac Standard) analyzes amodulation of an OFDM symbol that follows the L-SIG 224 in a receivedPHY data unit. If the OFDM symbol that follows the L-SIG 224 is BPSKmodulated, the legacy device determines that the received PHY data unitdoes not conform to the IEEE 802.11n Standard. On the other hand, if theOFDM symbol that follows the L-SIG 224 is Q-BPSK modulated, the legacydevice determines that the received PHY data unit does conform to theIEEE 802.11n Standard.

A device that conforms to the IEEE 802.11ac Standard also analyzes amodulation of an OFDM symbol that follows the L-SIG 224 in a receivedPHY data unit. If the OFDM symbol that follows the L-SIG 224 is Q-BPSKmodulated, the device determines that the received PHY data unitconforms to the IEEE 802.11n Standard. On the other hand, if the OFDMsymbol that follows the L-SIG 224 is BPSK modulated, the legacy devicedetermines that the received PHY data unit does conform to the IEEE802.11n Standard, e.g., the received PHY data may conform to the IEEE802.11a Standard or the IEEE 802.11ac Standard. The device that conformsto the IEEE 802.11ac Standard then analyzes a modulation of a next OFDMsymbol. If the next OFDM symbol is BPSK modulated, the device determinesthat the received PHY data unit does not conform to the IEEE 802.11acStandard. On the other hand, if the next OFDM symbol is Q-BPSKmodulated, the device determines that the received PHY data unitconforms to the IEEE 802.11ac Standard.

FIG. 6 is a block diagram of a wakeup packet 600 used in the exampleWLAN 110 of FIG. 1, according to an embodiment. The network interfacedevice 122 of the AP 114 is configured to generate and transmit thewakeup packet 600, according to an embodiment, e.g., to prompt thenetwork interface 142 of the client station 134 to transition from a lowpower state to an active state, according to an embodiment. The networkinterface device 142 of the client station 134-1 is also configured togenerate and transmit the wakeup packet 600, e.g., to prompt the networkinterface 142 of another client station 134 to wake up from the lowpower state, according to another embodiment.

The wakeup packet 600 includes the legacy 802.11 preamble 212 (discussedabove) and a payload 608. The legacy 802.11 preamble 212 enables IEEE802.11 stations (e.g., wireless communication devices that areconfigured to operate according to an IEEE 802.11 Standard) to detectthe wakeup packet 600 and estimate a duration of the wakeup packet 600for the purpose of reducing transmissions by the IEEE 802.11 stationsthat will collide with the wakeup packet 600, according to anembodiment.

In other embodiments, the wakeup packet 600 includes a legacy preamble(different than the legacy 802.11 preamble 212) that enables stationsthat conform to a different suitable wireless communication protocol(e.g., other than the IEEE 802.11 Standard) to detect the wakeup packet600 and estimate a duration of the wakeup packet 600 for the purpose ofreducing transmissions by such stations that will collide with thewakeup packet 600, according to an embodiment.

The payload 608 includes a wakeup preamble 624 and a wakeup packet body628. In an embodiment, the wakeup preamble 624 includes signals thatenable LP-WURs such as the LP-WUR 150 to detect the payload 608 of thewakeup packet 620 and to synchronize to the payload 608 of the wakeuppacket 620. In an embodiment, the wakeup packet body 628 includes anetwork address (e.g., a MAC address, an AID, or another suitablenetwork address) corresponding to a client station (or a group of clientstations) for which the wakeup packet 600 is intended. Referring now toFIG. 1D, the digital baseband circuitry 188 is configured to detect thewakeup packet 600 at least by detecting the wakeup preamble 624,according to an embodiment. The logic circuitry 192 is configured toprocess the wakeup packet body 628 to determine whether the wakeuppacket body 628 includes a network address (e.g., a MAC address, an AID,or another suitable network address) corresponding to the client station134-1.

In an embodiment, the wakeup packet 600 is generated and transmitted (bynetwork interface device 122 of the AP 114, etc.) using orthogonalfrequency domain multiplexing (OFDM) modulation. In one such embodiment,each of the fields of the wakeup packet 600 corresponds to one or moreOFDM symbols. For example, the L-SIG 224 corresponds to one OFDM symbol.

In an embodiment, network interface devices (such as the networkinterface device 142) of client stations are configured to receive,detect, and decode at least the legacy 802.11 preamble 212 of the wakeuppacket 600. In an embodiment, the legacy 802.11 preamble 212 is detectedand decoded at i) wireless network interface devices of communicationdevices that do not include a LP-WUR, and/or ii) at wireless networkinterface devices of communication devices that include a LP-WUR andwhose wireless network interface devices have already transitioned to anactive state from a low power state (based on a prior wakeup packet, forexample).

In an embodiment, the payload 608 of the wakeup packet 200 does notconform to a communication protocol that can be decoded and processed bya wireless network interface device such as the network interface device142. In one such embodiment, the network interface device 142 is notconfigured to (or fails to) decode and process at least a portion of thewakeup preamble 624 and the wakeup packet body 628 of the wakeup packet600.

The LP-WUR 150 of the client station 134-1 is not capable of detectingand/or decoding the payload legacy preamble 212 of the wakeup packet600, according to an embodiment. In other embodiments, however, theLP-WUR 150 of the client station 134-1 is configured to additionallyreceive, detect, and decode the legacy 802.11 preamble 212, or a portionthereof.

The payload 608 corresponds to a PPDU defined by a communicationprotocol (sometime referred to herein as a “wakeup packet communicationprotocol”) which is different than the communication protocol accordingto which the network interface device 142 is configured to operate(sometime referred to herein as a “WiFi communication protocol”),according to an embodiment. In an embodiment, the LP-WUR 150 cannotprocess and/or cannot correctly decode the legacy 802.11 preamble 212(or at least a portion thereof), and the network interface device 142cannot process and/or cannot correctly decode the payload 608 (or atleast a portion thereof).

In an embodiment, the payload 608 of the wakeup packet 600 occupies asmaller bandwidth (e.g., less than 50%, less than 25%, less than 20%,less than 10%) than the bandwidth of the legacy 802.11 preamble 212. Forinstance, in an embodiment, the legacy preamble 212 spans a 20 MHzbandwidth and the payload 608 spans 4 MHz. In an embodiment, the wakeuppacket 600 is generated and transmitted (by network interface device 122of the AP 114, network interface device 142 of the client station 134,etc.) using OFDM and the legacy 802.11 preamble 212 is transmitted usinga number of subcarriers that is greater than a number of subcarriersused for transmission of the payload 608. For instance, in anembodiment, the legacy 802.11 preamble 212 is transmitted over 52subcarriers within a 20 MHz wide communication channel, whereas thepayload 608 is transmitted over 13 subcarriers that span only a portion(e.g., a center 4 MHz portion) of the wider 20 MHz communicationchannel. In an embodiment, during the transmission of the payload 608,the remaining subcarriers corresponding to the wider 20 MHzcommunication channel are not used for transmission of any data and,therefore, do not include any transmitted signals.

A lower occupied bandwidth of a payload 608 of the wakeup packet 600 maylead to spurious detection of a communication protocol at a legacywireless network interface device such as a wireless network interfacedevice that is configured to i) operate according to the IEEE 802.11nStandard and ii) is not configured to operated according to the IEEE802.11ac Standard (hereinafter referred to as a “legacy 11n wirelessnetwork interface device”). For instance, as described above withrespect to the wakeup packet 600, the payload 608 is transmitted over anarrower communication channel (e.g., over a lower number ofsubcarriers) as compared to the legacy 802.11 preamble 212 that istransmitted over the wider 20 MHz communication channel. However, alegacy 11n wireless network interface device is configured to operateover the entirety of the wider communication channel. As a result, thelegacy 11n wireless network interface device may improperly detect themodulation of an OFDM symbol in the payload 608 that follows the L-SIG224. As merely an example, following the reception of the L-SIG 224, thelegacy 11n wireless network interface device will continue to processsignals over the entirety of 20 MHz communication channel, includingambient noise over subcarriers that do not include any data. The legacy11n wireless network interface then attempts to determine a modulationof the OFDM symbol that follows the L-SIG 224 in order to determine thecommunication protocol corresponding to the received wakeup packet 600.Ambient noise that is received along with the payload 608 may lead toincorrect detection of the communication protocol at the legacy 11nnetwork interface device.

In an embodiment, based on the detected modulations of L-SIG 224 and theOFDM symbol that immediately follows the L-SIG 224 (including theambient noise), the legacy 11n network interface device may sometimesincorrectly classify the wakeup packet 600 as conforming to the IEEE802.11n Standard. However, since the payload 608 of the wakeup packet600 does not conform to the IEEE 802.11 Standard, the legacy 11n networkinterface device will likely detect an error in data that the legacy 11nnetwork interface device decodes.

For instance, in an embodiment, the legacy 11n network interface devicemay incorrectly detect a modulation of the OFDM symbol that immediatelyfollows the L-SIG 224 as Q-BPSK, and thus classify the wakeup packet 600as conforming to the IEEE 802.11n Standard. The legacy 11n networkinterface device will then assume that the two OFDM symbols that followthe L-SIG 224 corresponds to the HT-SIG field 208 (FIG. 2), and thusprocesses the two OFDM symbols that follow the L-SIG 224 accordingly.The legacy 11n network interface device will then likely detect a cyclicredundancy check (CRC) error in the data decoded from the two OFDMsymbols (which the legacy 11n network interface device assumes are theHT-SIG field 208 (FIG. 2)) that follow the L-SIG 224. In response to thedetected CRC error, the network interface device 142 stops receiving andprocessing the PHY data unit 600 and determines whether thecommunication channel should be considered as idle before an end of theduration of the PHY data unit 600.

For example, the IEEE 802.11n Standard specifies that if a CRC error isdetected in the HT-SIG field 228, the legacy 11n network interfacedevice should monitor the received signal energy level and compares thereceived signal energy level to a threshold. If the received signalenergy level falls below the threshold, the IEEE 802.11n Standardspecifies that the legacy 11n network interface device should considerthe communication channel as being idle, even before the duration of thepacket has ended. Because the payload 608 of the wakeup packet 600 doesnot span the entire 20 MHz channel, there is a likelihood that thelegacy 11n network interface device will detect the received signalenergy level as falling below the threshold during reception of thepayload 608. Thus, there is a likelihood that, when the legacy 11nnetwork interface device receives the wakeup packet 600, the legacy 11nnetwork interface device will determine that the communication channelis idle prior to an end of the wakeup packet 600, and may thus initiatetransmission of a legacy 11n packet during transmission of the wakeuppacket 600. Such a transmission of a legacy 11n packet duringtransmission of the wakeup packet 600 may collide with the wakeup packet600 and interfere with the ability of LP-WURs to detect and/or correctlyprocess the wakeup packet 600.

To reduce the chance of a legacy 11n network interface deviceincorrectly classifying the wakeup packet 600 as conforming to the IEEE802.11n Standard, an additional field may be included between the legacy802.11 preamble 212 and the wakeup preamble 624. In an embodiment, thepresence of this additional field “spoofs” a recipient legacy 11nnetwork interface device into classifying the wakeup packet as notconforming to the IEEE 802.11n Standard.

FIG. 7 is a diagram of an example wakeup packet 700 used in the exampleWLAN 110 of FIG. 1, according to an embodiment. The network interfacedevice 122 of the AP 114 is configured to generate and transmit thewakeup packet 700, according to an embodiment. The network interfacedevice 142 of the client station 134-1 is also configured to generateand transmit the wakeup packet 700, e.g., to prompt another clientstation 134 to wake up from a low power state, according to anotherembodiment. The wakeup packet 700 is similar to the wakeup packet 600and like-numbered elements are not discussed for reasons of brevity.

A payload 710 of the of the wakeup packet 700 includes an extra field712 immediately following the legacy preamble 212 and occupying abandwidth that is equal to the bandwidth of the legacy preamble 212. Forinstance, in an embodiment, the legacy preamble 212 is transmitted tospan a 20 MHz communication channel and the extra field 712 is alsotransmitted to span the same 20 MHz communication channel. In anembodiment, the extra field 712 is modulated using a digital modulationtechnique that is different from Q-BPSK. For instance, as shown in FIG.8, the L-SIG 224 and the extra field 712 are both modulated using BPSK.

In an embodiment, the extra field 712 is a repeated L-SIG 224. In anembodiment, the extra field 712 is identical to at least a portion ofthe L-LTF 220. In other embodiments, the extra field 712 includes anyother suitable signal and/or information. In an embodiment, the extrafield 172 does not convey any useful information to recipientcommunication devices. In another embodiment, the extra field 172 doesconvey useful information to recipient communication devices. Forexample, in an embodiment, wakeup packet data (e.g., which includes anetwork address corresponding to an intended client station or stations)is encoded within/on a set of OFDM symbols that includes the extra field172 and the wakeup packet body 628.

In an embodiment, bits in the extra field 712 are scrambled. Forinstance, in an embodiment, the bits of the extra field 712 arescrambled using a scrambling technique that conforms to a standardwithin the IEEE 802.11 Standard family (e.g. IEEE 802.11a Standard, IEEE802.11n Standard, etc.). In another embodiment, a different scramblingtechnique is utilized for the bits in the extra field 712.

A legacy 11n network interface device that receives the wakeup packet700 detects the L-SIG 224 as being BPSK modulated. Following this, thelegacy 11n network interface device detects the extra field 712 as beingmodulated using a digital modulation technique that is different fromQ-BPSK and therefore classifies the wakeup packet 700 as not conformingto an IEEE 802.11n Standard. For example, the legacy 11n networkinterface device may assume that the wakeup packet 700 conforms to theIEEE 802.11a Standard. When the network interface device 142 detects aCRC error in an attempt to decode and process the payload 710 of thewakeup packet 700, the network interface device 142 stops processing thewakeup packet 700 and considers the communication channel as busy untilan estimated duration (determined using the L-SIG 224) of the wakeuppacket 700 has ended. Thus, the legacy 11n network interface device willnot initiate a transmission during the transmission of the wakeup packet700.

The presence of the extra field 712 with a defined modulation and thatspans a same wider communication channel as the legacy 802.11 preamble604 enables the legacy 11n network interface device to unambiguouslyclassify the wakeup packet 700 as not conforming to the IEEE 802.11nStandard, according to an embodiment.

In an embodiment, the wakeup packet 700 is generated and transmitted bynetwork interface device 122 of the AP 114, the network interface device142 of the client station 134, etc., using OFDM modulation. In one suchembodiment, each of the fields of the wakeup packet 700 correspond toone or more OFDM symbols. In an embodiment, for example, the L-SIG 224corresponds to one OFDM symbol and the extra field 712 corresponds toanother OFDM symbol.

In an embodiment, the LP-WUR 150 of the client station 134-1 isconfigured to receive, detect, and decode only the wakeup preamble 624and the wakeup packet body 628 of the wakeup packet 700, according to anembodiment. In other embodiments, however, the LP-WUR 150 of the clientstation 134-1 is configured to additionally receive, detect, and decodethe extra field 712.

In an embodiment, where the LP-WUR 150 is configured to decode the extrafield 712, the LP-WUR 150 operates over the entire bandwidth of the 20MHz communication channel. For instance, in an embodiment, the LP-WUR150 is configured to receive signals that span the entire 20 MHzcommunication channel that is used to transmit the extra field 712. Inone such embodiment, the extra field 712 further includes signals thatenable the LP-WUR 150 to perform receiver gain adjustment and/orsynchronization. In an embodiment where the extra field 712 includessignals for receiver gain adjustment and/or synchronization, a durationof the wakeup preamble 624 may be shortened as compared to the wakeuppacket 600 (FIG. 6) that does not include the extra field 712.

While the wakeup packet 700 has been described in the context of theIEEE 802.11 Standard family, in other embodiments, a similar techniqueis used to “spoof” communication devices in networks utilizing othercommunication protocols. For instance, one or more extra fields withparticular modulation schemes may be inserted into a packet that“spoofs” a receiving communication device into classifying the packet asnot conforming to a communication protocol that has disadvantageouscharacteristics (e.g., that may lead to an inadvertent determinationthat a communication channel is idle during transmission of a packet).

FIG. 9 is a flow diagram of an example method 900 for generating wakeuppackets, according to an embodiment. In some embodiments, the networkinterface device 122 of FIG. 1 is configured to implement the method900. The method 900 is described, however, in the context of the networkinterface device 122 merely for explanatory purposes and, in otherembodiments, the method 900 is implemented by another suitable device,such as the network interface device 142.

At block 904, the network interface device 122 generates a first portionof a wakeup packet. The first portion corresponds to a legacy PHYpreamble corresponding to a communication protocol. The first portionincludes a first OFDM symbol that spans a first bandwidth and ismodulated according to a modulation scheme. In an embodiment, the legacyPHY preamble is a legacy 802.11 preamble corresponding to the protocolspecified by the IEEE 802.11n Standard. The legacy PHY preamblecorresponds to other communication protocols as well, such as theprotocol specified by the IEEE 802.11ac Standard, the protocol specifiedby the IEEE 802.11ax Standard (now under development), etc., in someembodiments.

At block 908, the network interface device 122 generates a second OFDMsymbol, wherein the second OFDM symbol spans the first bandwidth and ismodulated according to the modulation scheme. In an embodiment, thesecond OFDM symbol corresponds to an extra symbol that follows legacyPHY preamble, such as the extra symbol 712 as described above withreference to FIG. 7. The second OFDM symbol is also modulated accordingto the BPSK modulation scheme, in an embodiment.

At block 912, the network interface device 122 generates a secondportion of the wakeup packet. The second portion spans a secondbandwidth that is less than the first bandwidth. The second portion ofthe wakeup packet is configured to prompt one or more wakeup radios atone or more respective communication devices to prompt one or morerespective network interfaces to transition from a low power state to anactive state. The second portion of the wakeup packet does not conformto the communication protocol to which the legacy PHY preamble conforms.In an embodiment, the second portion of the wakeup packet corresponds tothe wakeup preamble 624 and wakeup packet body 628 of the wakeup packet700 as described above. In an embodiment, the second portion of thewakeup packet is not configured to be decoded and processed by a networkinterface device that can decode and process data units conforming to astandard within the IEEE 802.11 Standard family.

At block 916, the network interface device 122 transmits the wakeuppacket. The transmitted wakeup packet includes the second OFDM symbolthat is transmitted, in time, between the first portion and the secondportion of the wakeup packet. The modulation of the second OFDM symbolaccording to the modulation scheme signals to communication devicesoperating according to the communication protocol that the wakeup packetdoes not conform to the communication protocol. For instance, modulationof both the L-SIG and modulation of the second OFDM symbol followingL-SIG according to a BPSK modulation scheme signals to a legacy 11nnetwork interface device that the wakeup packet does not conform to theIEEE 802.11n Standard.

Although the techniques described above were discussed in the context ofwakeup packets that can be decoded by LP-WURs, similar techniques can beutilized in other types of wireless communication systems that maycoexist with IEEE 802.11n/ac/ax wireless networks having legacy 11nwireless network interface device, in other embodiments. For example,other narrow band wireless communication networks in the 2.4 GHz and 5GHz bands may utilize a packet structure similar to those discussedabove so that legacy 802.11n network interface devices unambiguouslyclassify such packets as not conforming to the IEEE 802.11n Standard,according to other embodiments.

Embodiment 1

A method, comprising: generating, at the first communication device, afirst portion of a wakeup packet, wherein the first portion of thewakeup packet corresponds to a legacy physical layer protocol (PHY)preamble corresponding to a communication protocol, wherein the firstportion of the wakeup packet includes a first orthogonal frequencydivision multiplexing (OFDM) symbol that spans a first bandwidth and ismodulated according to a modulation scheme; generating, at the firstcommunication device, a second OFDM symbol, wherein the second OFDMsymbol spans the first bandwidth and is modulated according to themodulation scheme; generating, at the first communication device, asecond portion of the wakeup packet, wherein the second portion of thewakeup packet corresponds to a second bandwidth that is less than thefirst bandwidth, wherein the second portion of the wakeup packet isconfigured to prompt one or more wakeup radios at one or more respectivesecond communication devices to prompt one or more respective networkinterfaces to transition from a low power state to an active state, andwherein the second portion of the wakeup packet does not conform to thecommunication protocol; and transmitting, by the first communicationdevice, the wakeup packet, including transmitting, in time, the secondOFDM symbol between the first portion of the wakeup packet and thesecond portion of the wakeup packet, and wherein the modulation of thesecond OFDM symbol according to the modulation scheme signals to thirdcommunication devices operating according to the communication protocolthat the wakeup packet does not conform to the communication protocol.

Embodiment 2

The method of Embodiment 1, wherein the first OFDM symbol corresponds toa legacy signal (L-SIG) field that includes information indicating aduration of the wakeup packet.

Embodiment 3

The method of Embodiment 2, wherein the second OFDM symbol is arepetition of the first OFDM symbol.

Embodiment 4

The method of any of Embodiments 1-3, wherein: the first portion of thewakeup packet includes a third OFDM symbol corresponding to a legacylong training field (L-LTF), and the second OFDM symbol is a repetitionof the third OFDM symbol.

Embodiment 5

The method of Embodiment 1, wherein the second OFDM symbol of the wakeuppacket does not convey any useful information to the one or more secondcommunication devices.

Embodiment 6

The method of Embodiment 1, wherein the second OFDM symbol includes aplurality of information bits intended for the one or more secondcommunication devices.

Embodiment 7

The method of Embodiment 6, further comprising scrambling the pluralityof information bits.

Embodiment 8

The method of any of Embodiments 1-7, wherein the second portion of thewakeup packet includes at least a portion of a network identifiercorresponding to the one or more second communication devices.

Embodiment 9

The method of Embodiment 8, wherein the network identifier is amulticast address corresponding to the one or more second communicationdevices.

Embodiment 10

The method of any of Embodiments 1-7, wherein the second portion of thewakeup packet includes at least a portion of a network identifiercorresponding to a broadcast address.

Embodiment 11

The method of Embodiment 1, wherein generating the second OFDM symbolincludes generating the second OFDM symbol to include signals thatenable the one or more low power wakeup radios at the respective one ormore second communication devices to perform at least one of i) receivergain adjustment, and ii) synchronization.

Embodiment 12

The method of any of Embodiments 1-11, wherein the first OFDM symbol andthe second OFDM symbol are modulated according to a binary phase shiftkeying (BPSK) modulation scheme.

Embodiment 13

An apparatus, comprising: a network interface device associated with afirst communication device, wherein the network interface deviceincludes one or more integrated circuits (ICs) configured to: generate afirst portion of a wakeup packet, wherein the first portion of thewakeup packet corresponds to a legacy physical layer protocol (PHY)preamble corresponding to a communication protocol, wherein the firstportion of the wakeup packet includes a first orthogonal frequencydivision multiplexing (OFDM) symbol that spans a first bandwidth and ismodulated according to a modulation scheme, generate a second OFDMsymbol, wherein the second OFDM symbol spans the first bandwidth and ismodulated according to the modulation scheme, generate a second portionof the wakeup packet, wherein the second portion of the wakeup packetcorresponds to a second bandwidth that is less than the first bandwidth,wherein the second portion of the wakeup packet is configured to promptone or more wakeup radios at one or more respective second communicationdevices to prompt one or more respective network interfaces totransition from a low power state to an active state, and wherein thesecond portion of the wakeup packet does not conform to thecommunication protocol, and transmit the wakeup packet, includingtransmitting, in time, the second OFDM symbol between the first portionof the wakeup packet and the second portion of the wakeup packet, andwherein the modulation of the second OFDM symbol according to themodulation scheme signals to third communication devices operatingaccording to the communication protocol that the wakeup packet does notconform to the communication protocol.

Embodiment 14

The apparatus of Embodiment 13, wherein the first OFDM symbolcorresponds to a legacy signal (L-SIG) field that includes informationindicating a duration of the wakeup packet.

Embodiment 15

The apparatus of Embodiment 14, wherein the one or more ICs areconfigured to generate the second OFDM symbol as a repetition of thefirst OFDM symbol.

Embodiment 16

The apparatus of any of Embodiments 13-15, wherein the one or more ICsare configured to: generate the first portion of the wakeup packet toinclude a third OFDM symbol corresponding to a legacy long trainingfield (L-LTF), and generate the second OFDM symbol as a repetition ofthe third OFDM symbol.

Embodiment 17

The apparatus of Embodiment 13, wherein the second OFDM symbol of thewakeup packet does not convey any useful information to the one or moresecond communication devices.

Embodiment 18

The apparatus of Embodiment 13, wherein the second OFDM symbol includesa plurality of information bits intended for the one or more secondcommunication devices.

Embodiment 19

The apparatus of Embodiment 18, wherein the one or more ICs areconfigured to scramble the plurality of information bits.

Embodiment 20

The apparatus of any of Embodiments 13-19, wherein the one or more ICsare configured to generate the second portion of the wakeup packet toinclude at least a portion of a network identifier corresponding to theone or more second communication devices.

Embodiment 21

The apparatus of Embodiment 20, wherein the network identifier is amulticast address corresponding to the one or more second communicationdevices.

Embodiment 22

The apparatus of claim any of Embodiments 13-19, wherein the one or moreICs are configured to generate the second portion of the wakeup packetto include at least a portion of a network identifier corresponding to abroadcast address.

Embodiment 23

The apparatus of Embodiment 13, wherein the one or more ICs are furtherconfigured to generate the second OFDM symbol to include signals thatenable the one or more low power wakeup radios at the respective one ormore second communication devices to perform at least one of i) receivergain adjustment, and ii) synchronization.

Embodiment 24

The apparatus of any of Embodiments 13-23, wherein the one or more ICsare configured to modulate the first OFDM symbol and the second OFDMsymbol according to a binary phase shift keying (BPSK) modulationscheme.

Embodiment 25

A method, comprising: generating, at the first communication device, afirst portion of a packet intended for one or more second communicationdevices, wherein the first portion of the packet corresponds to a legacyphysical layer protocol (PHY) preamble corresponding to a firstcommunication protocol, wherein the first portion of the packet includesa first orthogonal frequency division multiplexing (OFDM) symbol thatspans a first bandwidth and is modulated according to a modulationscheme; generating, at the first communication device, a second OFDMsymbol, wherein the second OFDM symbol spans the first bandwidth and ismodulated according to the modulation scheme; generating, at the firstcommunication device, a second portion of the packet, wherein the secondportion of the packet conforms to a second communication protocolconfigured for communications on one or more channel bandwidths that arenarrower than the first bandwidth, wherein the second portion of thepacket corresponds to a second bandwidth that is less than the firstbandwidth, and wherein the second portion of the packet does not conformto the first communication protocol; and transmitting, by the firstcommunication device, the packet, including transmitting, in time, thesecond OFDM symbol between the first portion of the packet and thesecond portion of the packet, and wherein the modulation of the secondOFDM symbol according to the modulation scheme signals to thirdcommunication devices operating according to the first communicationprotocol that the packet does not conform to the first communicationprotocol.

Embodiment 26

The method of Embodiment 25, wherein the first OFDM symbol correspondsto a legacy signal (L-SIG) field that includes information indicating aduration of the packet.

Embodiment 27

The method of Embodiment 26, wherein the second OFDM symbol is arepetition of the first OFDM symbol.

Embodiment 28

The method of any of Embodiments 25-27, wherein: the first portion ofthe packet includes a third OFDM symbol corresponding to a legacy longtraining field (L-LTF), and the second OFDM symbol is a repetition ofthe third OFDM symbol.

Embodiment 29

The method of Embodiment 25, wherein the second OFDM symbol of thepacket does not convey any useful information to the one or more secondcommunication devices.

Embodiment 30

The method of Embodiment 25, wherein the second OFDM symbol includes aplurality of information bits intended for the one or more secondcommunication devices.

Embodiment 31

The method of Embodiment 30, further comprising scrambling the pluralityof information bits.

Embodiment 32

The method of any of Embodiments 25-31, wherein the second portion ofthe packet includes at least a portion of a network identifiercorresponding to the one or more second communication devices.

Embodiment 33

The method of Embodiment 32, wherein the network identifier is amulticast address corresponding to the one or more second communicationdevices.

Embodiment 34

The method of any of Embodiments 25-31, wherein the second portion ofthe packet includes at least a portion of a network identifiercorresponding to a broadcast address.

Embodiment 35

The method of Embodiment 25, wherein generating the second OFDM symbolincludes generating the second OFDM symbol to include signals thatenable one or more network interfaces at the respective one or moresecond communication devices to perform at least one of i) receiver gainadjustment, and ii) synchronization.

Embodiment 36

The method of any of Embodiments 25-35, wherein the first OFDM symboland the second OFDM symbol are modulated according to a binary phaseshift keying (BPSK) modulation scheme.

Embodiment 37

An apparatus, comprising: a network interface device associated with afirst communication device. The network interface device includes one ormore integrated circuits (ICs) configured to: generate a first portionof a packet intended for one or more second communication devices,wherein the first portion of the packet corresponds to a legacy physicallayer protocol (PHY) preamble corresponding to a first communicationprotocol, wherein the first portion of the packet includes a firstorthogonal frequency division multiplexing (OFDM) symbol that spans afirst bandwidth and is modulated according to a modulation scheme;generate a second OFDM symbol, wherein the second OFDM symbol spans thefirst bandwidth and is modulated according to the modulation scheme;generate a second portion of the packet, wherein the second portion ofthe packet conforms to a second communication protocol configured forcommunications on one or more channel bandwidths that are narrower thanthe first bandwidth, wherein the second portion of the packetcorresponds to a second bandwidth that is less than the first bandwidth,and wherein the second portion of the packet does not conform to thefirst communication protocol; and transmit the packet, includingtransmitting, in time, the second OFDM symbol between the first portionof the packet and the second portion of the packet, and wherein themodulation of the second OFDM symbol according to the modulation schemesignals to third communication devices operating according to the firstcommunication protocol that the packet does not conform to the firstcommunication protocol.

Embodiment 38

The apparatus of Embodiment 37, wherein the first OFDM symbolcorresponds to a legacy signal (L-SIG) field that includes informationindicating a duration of the packet.

Embodiment 39

The apparatus of Embodiment 38, wherein the one or more ICs areconfigured to generate the second OFDM symbol as a repetition of thefirst OFDM symbol.

Embodiment 40

The apparatus of any of Embodiments 37-39, wherein the one or more ICsare configured to: generate the first portion of the packet to include athird OFDM symbol corresponding to a legacy long training field (L-LTF),and generate the second OFDM symbol as a repetition of the third OFDMsymbol.

Embodiment 41

The apparatus of Embodiment 37, wherein the second OFDM symbol of thepacket does not convey any useful information to the one or more secondcommunication devices.

Embodiment 42

The apparatus of Embodiment 37, wherein the second OFDM symbol includesa plurality of information bits intended for the one or more secondcommunication devices.

Embodiment 43

The apparatus of Embodiment 42, wherein the one or more ICs areconfigured to scramble the plurality of information bits.

Embodiment 44

The apparatus of any of Embodiments 37-43, wherein the one or more ICsare configured to generate the second portion of the packet to includeat least a portion of a network identifier corresponding to the one ormore second communication devices.

Embodiment 45

The apparatus of Embodiment 44, wherein the network identifier is amulticast address corresponding to the one or more second communicationdevices.

Embodiment 46

The apparatus of claim any of Embodiments 37-43, wherein the one or moreICs are configured to generate the second portion of the packet toinclude at least a portion of a network identifier corresponding to abroadcast address.

Embodiment 47

The apparatus of Embodiment 13, wherein the one or more ICs are furtherconfigured to generate the second OFDM symbol to include signals thatenable one or more network interface devices at the respective one ormore second communication devices to perform at least one of i) receivergain adjustment, and ii) synchronization.

Embodiment 24

The apparatus of any of Embodiments 37-47, wherein the one or more ICsare configured to modulate the first OFDM symbol and the second OFDMsymbol according to a binary phase shift keying (BPSK) modulationscheme.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. The software or firmware instructions mayinclude machine readable instructions that, when executed by one or moreprocessors, cause the one or more processors to perform various acts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), a programmable logic device (PLD), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method, comprising: generating, at the firstcommunication device, a first portion of a wakeup packet, wherein thefirst portion of the wakeup packet corresponds to a legacy physicallayer protocol (PHY) preamble corresponding to a communication protocol,wherein the first portion of the wakeup packet includes a firstorthogonal frequency division multiplexing (OFDM) symbol that spans afirst bandwidth and is modulated according to a modulation scheme;scrambling, at the first communication device, a plurality ofinformation bits to generate scrambled information bits, the pluralityof information bits intended for the one or more second communicationdevices; generating, at the first communication device, a second OFDMsymbol to include the scrambled information bits, wherein the secondOFDM symbol spans the first bandwidth and is modulated according to themodulation scheme; generating, at the first communication device, asecond portion of the wakeup packet, wherein the second portion of thewakeup packet corresponds to a second bandwidth that is less than thefirst bandwidth, and wherein the second portion of the wakeup packetdoes not conform to the communication protocol; and transmitting, by thefirst communication device, the wakeup packet, including transmitting,in time, the second OFDM symbol between the first portion of the wakeuppacket and the second portion of the wakeup packet, and wherein themodulation of the second OFDM symbol according to the modulation schemesignals to third communication devices operating according to thecommunication protocol that the wakeup packet does not conform to thecommunication protocol.
 2. The method of claim 1, wherein: the firstOFDM symbol corresponds to a legacy signal (L-SIG) field that includesinformation indicating a duration of the wakeup packet; and scramblingthe plurality of information bits to generate scrambled information bitscomprises scrambling information bits of the L-SIG field.
 3. The methodof claim 1, wherein: scrambling the plurality of information bits togenerate scrambled information bits comprises using a scramblingtechnique defined by the IEEE 802.11 Standard.
 4. The method of claim 1,wherein: generating the first portion of the wakeup packet comprisesgenerating the first portion of the wakeup packet to include a thirdOFDM symbol corresponding to a legacy long training field (L-LTF); andtransmitting the wakeup packet comprises transmitting, in time, thethird OFDM symbol prior to the first OFDM symbol.
 5. The method of claim1, wherein the second portion of the wakeup packet includes at least aportion of a network identifier corresponding to the one or more secondcommunication devices.
 6. The method of claim 5, wherein the networkidentifier is a multicast address corresponding to the one or moresecond communication devices.
 7. The method of claim 1, wherein thesecond portion of the wakeup packet includes at least a portion of anetwork identifier corresponding to a broadcast address.
 8. The methodof claim 1, wherein generating the second OFDM symbol includesgenerating the second OFDM symbol to include signals that enable the oneor more low power wakeup radios at the respective one or more secondcommunication devices to perform at least one of i) receiver gainadjustment, and ii) synchronization.
 9. The method of claim 1, wherein:generating the first portion of the wakeup packet comprises generatingthe first OFDM symbol according to a binary phase shift keying (BPSK)modulation scheme; and generating the second OFDM symbol comprisesgenerating the second OFDM symbol according to the BPSK modulationscheme.
 10. A first communication device, comprising: a wireless networkinterface device having one or more integrated circuit (IC) devicesconfigured to: generate a first portion of a wakeup packet, wherein thefirst portion of the wakeup packet corresponds to a legacy physicallayer protocol (PHY) preamble corresponding to a communication protocol,wherein the first portion of the wakeup packet includes a firstorthogonal frequency division multiplexing (OFDM) symbol that spans afirst bandwidth and is modulated according to a modulation scheme,scramble a plurality of information bits to generate scrambledinformation bits, the plurality of information bits intended for the oneor more second communication devices, generate a second OFDM symbol toinclude the scrambled information bits, wherein the second OFDM symbolspans the first bandwidth and is modulated according to the modulationscheme, generate a second portion of the wakeup packet, wherein thesecond portion of the wakeup packet corresponds to a second bandwidththat is less than the first bandwidth, and wherein the second portion ofthe wakeup packet does not conform to the communication protocol, andcontrol the wireless network interface device to the wakeup packet,including transmitting, in time, the second OFDM symbol between thefirst portion of the wakeup packet and the second portion of the wakeuppacket, and wherein the modulation of the second OFDM symbol accordingto the modulation scheme signals to third communication devicesoperating according to the communication protocol that the wakeup packetdoes not conform to the communication protocol.
 11. The firstcommunication device of claim 10, wherein: the first OFDM symbolcorresponds to a legacy signal (L-SIG) field that includes informationindicating a duration of the wakeup packet; and the one or more ICdevices are configured to scramble information bits of the L-SIG fieldto generate the scrambled information bits.
 12. The first communicationdevice of claim 10, wherein the one or more IC devices are configuredto: scramble the plurality of information bits to generate scrambledinformation bits using a scrambling technique defined by the IEEE 802.11Standard.
 13. The first communication device of claim 10, wherein theone or more IC devices are configured to: generate the first portion ofthe wakeup packet to include a third OFDM symbol corresponding to alegacy long training field (L-LTF); and control the wireless networkinterface device to transmit, in time, the third OFDM symbol prior tothe first OFDM symbol.
 14. The first communication device of claim 10,wherein the one or more IC devices are configured to generate the secondportion of the wakeup packet to include at least a portion of a networkidentifier corresponding to the one or more second communicationdevices.
 15. The first communication device of claim 14, wherein thenetwork identifier is a multicast address corresponding to the one ormore second communication devices.
 16. The first communication device ofclaim 10, wherein the one or more IC devices are configured to generatethe second portion of the wakeup packet to include at least a portion ofa network identifier corresponding to a broadcast address.
 17. The firstcommunication device of claim 10, wherein the one or more IC devices areconfigured to generate the second OFDM symbol to include signals thatenable the one or more low power wakeup radios at the respective one ormore second communication devices to perform at least one of i) receivergain adjustment, and ii) synchronization.
 18. The first communicationdevice of claim 10, wherein the one or more IC devices are configuredto: generate the first OFDM symbol according to a binary phase shiftkeying (BPSK) modulation scheme; and generate the second OFDM symbolaccording to the BPSK modulation scheme.
 19. The first communicationdevice of claim 10, wherein the wireless network interface devicecomprises one or more transceivers.
 20. The first communication deviceof claim 19, further comprising: one or more antennas coupled to the oneor more transceivers.